This invention relates to adhesive compositions, and more particularly adhesive compositions used for releasably adhering packaging materials.
Adhesive compositions used in the packaging of sterile medical products must exhibit certain special properties. Sterile medical devices such as catheters are packaged between a spun-bonded polyolefin fiber non-woven fabric and an ethylene vinyl acetate copolymer film. The spun-bonded polyolefin fiber non-woven fabric is thermoformed, filled a medical device and sealed, around the periphery of the fabric, to the ethylene vinyl acetate copolymer film with an adhesive. The medical device is sterilized in the package by exposure to ethylene oxide gas or by irradiation with gamma radiation or an electron beam. The adhesive must securely bond the spun-bonded polyolefin fiber fabric to the ethylene vinyl acetate copolymer film, while allowing the ethylene vinyl acetate copolymer film to be peeled away from the spun-bonded polyolefin fiber fabric without causing the fabric to tear. It is also highly desirable that the adhesive leave a white transfer layer of material along the perimeter of the ethylene vinyl acetate copolymer film to indicate that a sterile seal was achieved.
A suitable adhesive for packaging of sterile medical devices between a thermoformed propylene fiber non-woven fabric and an ethylene vinyl acetate copolymer film must be adhesively strong, but cohesively weak. A suitable adhesive has a peel strength of about one pound per inch. Because the adhesive is applied over the entire surface of the ethylene vinyl acetate copolymer film, it is important that the adhesive have sufficient clarity so that the medical device in the package can be easily seen. This is especially important when the medical device is color-coded. Also, it is highly desirable that the adhesive have a relatively low coefficient of friction and relatively low tackiness. The requirements for low coefficient of friction and low tackiness are due largely to the expectations of medical personnel opening the package to retrieve a medical device.
It is preferred that the ethylene vinyl acetate copolymer film is sufficiently smooth and has sufficiently low tackiness to prevent the polyethylene vinyl acetate copolymer film from abrading or sticking to latex gloves, clothing or the like.
The adhesive compositions that have been used to adhere spun-bonded polyolefin fiber non-woven fabric to a polyethylene vinyl acetate copolymer film for medical device packaging have comprised a blend of polyethylene vinyl acetate and wax. It has been found that the known polyethylene vinyl acetate/wax blends tend to cause the lighter weight spun-bonded polyolefin fiber non-woven fabrics that are currently preferred to tear when peeled open. Also, the known adhesive blends do not exhibit other optimum properties, such as low coefficient of friction and low tackiness. Accordingly, there is a need for improved adhesive compositions for medical device product packaging that exhibit an adhesive strength of from about 0.75 to about 1.75 pounds per inch over a range of heat sealing temperatures from about 115xc2x0 C. to about 135xc2x0 C., while also exhibiting suitable transfer properties (to indicate a continuous sterile seal along the perimeter of the package), clarity, low coefficient of friction, and low tackiness. In order to meet processing requirements during co-extrusion of the polyethylene vinyl acetate copolymer film and adhesive, it is also desirable that the adhesive composition have a melt index of about 20 or less.
The adhesive compositions of this invention are specifically formulated for use in bonding a spun-bonded polyolefin fiber, non-woven fabric to a polyethylene vinyl acetate film for medical product packaging. In particular, the adhesive compositions of this invention are specially formulated to exhibit a desirable peel strength, transfer properties, clarity, low coefficient of friction, and low tackiness when used for bonding a spun-bonded polyolefin fiber, non-woven fabric to an ethylene vinyl acetate copolymer film.
The objectives of this invention have been met with an adhesive composition containing from about 5 to about 65 percent by weight of a low density polyethylene; from about 35 to about 90 percent by weight of an ethylene vinyl acetate copolymer; and from about 5 to about 65 percent by weight of a linear block copolymer having at least one vinyl substituted aromatic hydrocarbon polymer block and at least one polyolefin polymer block made from an aliphatic conjugated diene. The total polymer content of the composition is at least 90 percent by weight.
In one aspect of the invention, a package for medical products is provided. The package includes a spun-bonded polyolefin fiber, non-woven fabric bonded to a polyethylene vinyl acetate copolymer film with an adhesive composition containing from about 5 to about 65 percent by weight of a low density polyethylene; from about 35 to about 90 percent by weight of an ethylene vinyl acetate copolymer; and from about 5 to about 65 percent by weight of a linear block copolymer having at least one vinyl substituted aromatic hydrocarbon polymer block and at least one polyolefin polymer block made from an aliphatic conjugated diene.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.